One cylinder, two pistons. - Dave
Further to the discussion in the selby rail crash thread: I thought I'd share the debate under a more interesting title!

For the back ground go to:

John S: Don't think so John. I *think* I saw it in motorcycle news.

IIRC it was in a racing formula where less cylinders confered some sort of weight advantage/disadvantage.

The design was to get around this rule. Either by claimng a two was a four or vice versa.

The cylinder was like a pair of bog roll cylinders taped together with th ejoined bit 'missing' and the 'two' pistons were directly linked and went up and down together.

I'm not sure it wasn't an April fool but it seemed genuine at the time.

I don't know what era the bike is/was from.

I reckon Doug is on the right track with the Honda. I'm 30 per cent sure it *was* a Honda.

Maybe I dreamed it?
Re: One cylinder, two pistons. - Mark
Fairly sure it was a German manufacturer possibly DKW, however I can't find my classic motorcycle encyclopedia at the moment.

as ever

Re: One cylinder, two pistons. - Alwyn

Der Kleiner Wunder. (Spellcheck from Andy Bairsto required)
Re: One cylinder, two pistons. - John Davis
I'm sure you are right Mark. From the 50's I remember the EMC Puch (Erlich Motorcycles ?) where there was a new front fork design, ie, swinging arm, and they used a "split single" engine of German manufacture, possible DKW. Two pistons, in seperate, parallel, vertical cylinders, with the rear cylinder (I think) charging the front cylinder. Two stroke cycle with the rear cylinder acting like the pressurised crankcase of a conventional two stroke.
Re: One cylinder, two pistons. - Mark

this was Dr Joes obsession, in the late 40's he produced a 350 2 stroke engine with 2 pistons on a forked con rod with a common combustion chamber.

By 1960 he had support from De Haviland and was racing in the world championship series with some success.

I eventually found my encyclopedia as you may well surmise.

as ever

Re: One cylinder, two pistons. - Peter
The Deltic locomotives of British Rail used this system. The engine was arranged in a triangular shape with a crankshaft at each corner, two pistons shared a common cylinder but drove a different crankshaft.

I also believe they were a two stroke diesel adapted from a pre war German design that ended up in German torpedo boats and Napier had the UK patents before the war.

After the war Napier searched around for a suitable use for the engines and one use was in railway locomotives. Whilst only 22 Deltics were ever built the engine was successful but BR took the decision to use low rev. diesels on future engines. the Deltic engine being a high rev. device. The decision was based on operating costs.
Re: One cylinder, two pistons. - Simon Butterworth
There are a signifcant number of the 22 in preservation including several allowed out on the main line. Fantastic machines, magical noise.
Re: One cylinder, two pistons. - OldOiler
When I worked ina MOD test house we had one of these DELTIC's on a test bed and yes they used to "bark" when on song!! - we were experimenting with fuels at the time.
a previous person was talking about torpedo engines - these where quite a lump - all confined in a 24" dia tube about 8 cylinders if I remeber correctly fired by "otto fuel" with a 6000 psi air res. the highest HP I have dealt with was a single shaft turbine with 1000 hp + all confined within 24" dia using otto + another additive - more powerful than the warhead !!

Re: One cylinder, two pistons. - Mark (Brazil)>DKW>Vostok
Re: One cylinder, two pistons. - John S

Yes, your description and the replies and sites here do remind me about this development in motorcycles, a rather different idea to the opposed piston diesels.


Deltic engine - Kev
Sorry, not worked out fancy links

Re: Deltic engine - Bill Doodson

Are you talking about "bog rolls" joined end to end or side to side? If you mean side to side, OO with the top and the bottom joined to make a sort of oval like a running track then this was a Honda racing engine for motorcycle use. It was never totally succesful as I recall but did win some races.

Honda engine - J Bonington Jagworth
You mean oval cylinders/pistons? If memory serves, this was to enable more valves/cylinder (8, I think) although there may have been other features. It was all pretty secret at the time! Simple thermodynamics prevented it from beating the 2-strokes, I believe, although it was a brave effort.

Leads me to conclude that GP racing should be based simply on an allowed quantity of prescribed fuel, all other factors at the discretion of the entrant. Would make for more interesting vehicles, IMHO.
One cylinder three pistons - Bill Doodson
Or how about the engine with one cylinder and 3 pistons! I have mentioned it before I think on a deltic thread.

Re: One cylinder, two pistons. - Paul Richards
The Rootes Group made a two stroke Commer Lorry with horizontally opposed pistons within the sama cylinder and two geared crankshafts. The noise from this engine under full load was absolutely magic and could be heard form half a mile away. I don`t think the plod would take too kindly to it today!!
Re: One cylinder, two pistons. - david
Used to drive one with 2 stock cars on the back

It had a Rootes supercharger & a 5 speed box when 4 was normal

I used to love getting in the outside lane and blowing off sports cars at the lights.
Re: One cylinder, two pistons. - Dave at Home (Chateau Dave)
10/10 Bill Doodson!

You know exactly what I mean!

Joined like that - OO - but closer so they merge with two pistons.

Thanks mate I reckoned it was a Honda!

Care to post a link?
Re: One cylinder, two pistons. - J Bonington Jagworth
I found some more stuff on Napier that makes fascinating reading (4-valves per cylinder in 1916!) on

Aero engine design does make one wonder what car engine designers do for a living, although I guess they're contrained by accountants these days.

For more reading, see LJK Setright's 'Some Unusual Engines'. There's some weird and wonderful stuff out there...

(Note to Martyn - I accidentally posted this on an old thread, just now. I'm not trying to clog up your system, honestly!)
Re: One cylinder, two pistons. - Bill F
Just joined the chat room and saw the subject.
There was a 6-cylinder Junkers Jumo engine with opposed pistons and two crankshafts that bombed Britain in WW2. THere is now in production a 2-cylinder 100HP version powering a Luscombe aircraft: it is made by Diesel Air and can be seen at My company FairDiesel Limited is making a barrel-engine version, where the pistons drive the main shaft via cams. If interested, contact me on for pictures and animations. Bill F
Re: One cylinder, two pistons. - J Bonington Jagworth
"...constrained..." that should be!

I'd ask for an edit button, but then we'd be denied such treats as "anall day benders"...
Re: Honda engine - Steve
The oval cylinder was a Honda design for a GP Bike that could compete against the two strokes in the late 1960s. I think it only raced for one or two seasons and was not very successful. The other two cylinder two stroke mentioned was a pre war DKW which raced at the IOM TT and was very successful. The additional cylinder was used as a charging cylinder to compress the fuel/air in place of the usual crankcase compression. It was rumered that the bike could be heard in Liverpool when racing in the TT. The Bike was due to compete again after the war but new rules which classed the charging cylinder as a supercharger prevented this. The same fate finished the AJS porcupine as a competitive machine when supercharging was outlawed.
Re: Honda engine - paulb {P}
I remember seeing a picture of an engine in a Honda brochure about 8 years ago, which had oval pistons with 2 con-rods each, thus allowing a 32-valve V4. AIR it was actually fitted to a particular bike, but can't for the life of me remember what that was.
Re: Honda engine - Edward
It was the NR750 and was a sort of technology demontrator for Honda (single sided swing arm, the 32 valve engine etc.). It was on sale for road use but cost a ferocious amount of money.
One cylinder, two pistons. - ndbw
Does anyone else out there remember the Trojan Vans used by Brooke-Bond Tea Co. These had two pistons on a common crankshaft,the secound piston acting as a charging device for the one power piston.These were single cylinder and had a very long life in fact a bakery Grooms of Erith in Kent had a contract with Brook-Bond to buy the vans when they were replaced and use them for door to door deliveries.

One cylinder, two pistons. - wemyss
Yes I remember them very well if its what I?m thinking off. Weren?t they made by Jowett who who well known for the Javelin?. I knew they were two cylinder but not that one piston only supplied the power.
Travelled many miles in one as an apprentice in the 50s and recall they had a distinctive sound.
Very uncomfortable crouched in the back along with another apprentice amidst a pile of tools and materials.
The plumber who drove it was the worlds worst driver and it was our job to hold all the traffic up on the A6 while he reversed it into the works yard. The gates were wide enough to take a Pickfords heavy haulage unit but Bill needed all that and more. However he did become Derby County Chairman at one period.
There were quite a few of these vans about at this time and as I recall were all in the same shade of grey.
One cylinder, two pistons. - malbeare
Have a look at

(1)The 6-stroke engine is fundamentally superior to the 4- stroke because the head is a net contributor to, and an integral part of the power generation within the engine.
(2)The 6stroke is thermodynamically more efficient because the change in volume of the power stroke is greater than the intake, compression, & exhaust strokes.
(3)The compression ratio can be increased because of the absence of hot spots.
(4)The rate of change in volume during the critical combustion period is less than in a 4stroke.
(5)The absence of valves within the combustion chamber allows design freedom.
(6) A one-piece engine from crankshaft to upper shaft becomes feasible. No head gasket.
(7)Fewer components, 15 per cylinder compared to 40 for a 4-stroke. Therefore the cost of manufacture is much less.
(8)Can be fitted to standard engine blocks so the market is much larger than the OEM sector , also includes the retrofit aftermarket sector.
The engine has proven to be robust on the race track, & have significant advantages over 4-strokes
(1)The valving is desmodromic
(2)There are no valves to drop or bounce.
(3)The rev limit is only what the bottom end can stand.
(4)Gas flow on intake increase of 20%.
(5)No possibility of engine damage if the timing belt slips or snaps
(6)The reed valves are so close to the intake ports that their tips become the virtual port opening. This achieves variable port area & variable engine demand valve timing. The tips open late & small amounts with low throttle settings & open early & fully at full throttle

thanks folks malbeare

One cylinder, two pistons. - Matt
Have a gander at this:
Very informative!


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